Simultaneous transmit, and receive (STAR) refers to the ability of a radio frequency (RF) circuit, device, or system to transmit and receive at the same time, in the same frequency band, with adequate performance in the receiver. Such capability is desired for applications such as, for example, cognitive radio and full-duplex communications systems. In a conventional approach, RF transmit and receive operations within a particular frequency band are performed at different times. This is because transmit energy from a transmit antenna will typically leak into the front end of a collocated receiver and overdrive the receiver if transmit and receive operations are performed concurrently. This transmitter leakage can mask the desired receive signals, thus making it difficult or impossible to detect, demodulate, and decode the signals. For STAR operation to be possible, therefore, a certain minimum level of isolation must be main tamed between a transmit antenna and a receive antenna.
Antennas have been designed in the past that are capable of supporting STAR operation. However, such antennas have invariably been of relatively low bandwidth. There is a need for antennas that are capable of simultaneous transmit and receive operation over wider bandwidths.